Method of and means for treating gases



Aug. 3, 1954 s. c. COLLINS METHOD OF AND MEANS FOR TREATING GASESOriginal Filed Oct. 18, 1949' I 2 Sheets-Sheet J.

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Patented Aug. 3, 1954 METHOD OF AND MEANS FOR TREATING GASE Samuel 0.Collins, Watertown, Mass, assignor to Joy Manufacturing Company,Pittsburgh, Pa., a. corporation of Pennsylvania Original applicationOctober 18 1949, Serial No. 122,077. Divided and this applicationOctober 1, 1953, Serial No. 383,541

35 Claims. 1

This invention relates to improvements in methods of and means fortreating gases.

It Will herein be described particularly in its application to theproduction of substantially pure oxygen from air, but this is butillustrative, because the process and apparatus disclosed may be used,with appropriate adaptations, with various gases to be processed, toproduce various particularly desired products which are constituents ofthe gases to be treated. Under some circumstances the desired productmay be delivered at a relatively very high pressure and under others ata pressure of a few atmospheres.

It is very common, in the production of oxygen by a process involvincooling and rectification of compressed air, to have it desirable tohave the oxygen available in gaseous form at a pressure substantiallyabove column pressure but, on the other hand, much below cylinderpressure (Cylinder pressure is on the order of 2000 p. s. i.) Forexample, oxygen may be desired at a pressure on the order of 50 p. s.i., though this is but illustrative, and indeed the reference to oxygenis but illustrative also, because other gases which may be obtained by asimilar process may also be desired at pressures above column pressure.Refrigeration can be saved, taking the case of oxygen for purposes ofillustration, by taking gaseous rather than liquid oxygen from a pointin a column above the level of the liquid oxy en therein and boostingthe pressure from the few p. s. i. (perhaps 5) which exists at thatpoint in the column, to the desired delivery pressure by the use of acompressor. This is, however, objectionable because of the additionalpower required and because of the size of the gaseous oxygen compressorwhich would be required. It is, I have found, much preferable to takeliquid oxygen from the column and to pump it at the desired pressure tothe oxygen supply line. This permits the use of much smaller pumpingequipment. It would, however, result in wasted refrigeration if someprovision were not made for using the heat of vaporization of liquidoxygen in some manner. This heat of vaporization, I have found, may beutilized by condensing an equivalent amount of air on its Way to, therectifier, as by bringing an appropriate amount of air at an .ppropriatepressure and temperature into heat exchange relation with the leavingoxygen at a pressure substantially above column pressure, and utilizingthe heat of vaporization to effect the liquefaction .of compressedair.For example, compressed air at about 158 p. s. i. may be sup- ;plied'toa suitableevaporator-condenser and be condensed, when the temperature isreduced to, say, 112 K. and the heat removed to effect the condensationis absorbed by heat transfer within the evaporator-condenser by anoutwardly flowing stream of initially liquid oxygen, and the oxygen maybe vaporized at 107 K. and p. s. i. by the heat absorbed from thecompressed air as the latter is liquefied. Such an arrangement willinvolve a minimum loss of refrigeration and concurrently avoid the needfor a larger-size oxygen pump, and there will be a conservation of powerbecause the work of raising the pressure of liquid oxygen through apressure range of 40 p. s. i. or so will be much less than is requiredsimilarly to increase the pressure of an equal mass of gaseous oxygen.It will be evident that with a higher compressed air supply pressure,liquid oxygen at a higher pressure may be vaporized in theevaporator-condenser. It will also be evident that even if the deliverypressure of the oxygen (or other desired gas) should have to besubstantially in excess of the pressure at which the liquid oxygen mightbe vaporized in the evaporator-condenser, refrigeration could be savedand the size and power requirements of the pump for gaseous oxygen whichmight be needed to bring the oxygen delivery pressure to the desiredvalue might be made smaller, provided the foregoing procedure wereadopted as a preliminary to the compression of the gaseous oxygen fromthe pressure at which it would leave the evaporator-condenser to thepressure desired in the oxygen supply line.

It will be evident that the weight of the air put through theevaporator-condenser in heat exchange relation with leaving oxygen neednot be just such as to be completely liquefied by the refrigerationprovided by vaporizing the oxygen, but that more than just that weightof air can be put through the evaporator-condenser, and have completeliquefaction effected as later explained. Moreover, the air usuallypassed through the evaporator-condenser may be diverted to the expansionengine when, due to fortuitous circumstances, the expansion enginerequires more air, and thus a more flexible system may be provided.

It is thus among the objects of the invention to provide a simple,compact, flexible apparatus for the efiicient separation of gases, inwhich the requisite refrigeration is provided by a portion of theapparatus, in which the desired end product may be produced with apurity of 99.5% or better, in which, due to the effective removal ofimpurities and the resultant avoidance of plugging of portions of theapparatus by the 3 impurities, longer periods of operation may bepossible, in which the accumulation of liquid for the placing of theunit in operation may be speeded up, and in which refrigeration may beconserved and the end product, in the illustrative embodiment oxygen,may be obtained with apparatus of minimum size and power consumption ata pressure substantially above column pressure.

A further object of the invention is to provide an improved method forthe separation of gases, and more particularly for the separation ofair, and the recovery in a desired nearly pure state of a constituentthereof. Other objects and advantages of the invention will hereinafterappear.

In the accompanying drawings, in which apparatus by which the methodaspect of the invention may be practiced, and in which single and doublecolumn apparatus embodiments of the invention are shown for purposes ofillustration:

Fig. 1 is a diagrammatic view of a single column embodiment, and

Fig. 2 is a similar view of a double column embodiment of the invention.

Referring first to the system shown in Fig. l of the drawings, air at atemperature of approximately 300 K. and a pressure of 160 p. s. i. (allpressures are gauge unless otherwise indicated) may be delivered, asfrom a suitable air compressor (not shown), through a conduit H to avalve mechanism generally designated l2, and

the efliuent (mainly nitrogen) leaving the apparatus may be dischargedto the atmosphere through a conduit l3. The valve mechanism i2 is of themechanically actuated type, and is periodically moved by power, and witha snap action, to reverse the connections of the conduits H and [3 witha pair of conduits i5 and |5 which lead from the casing of the valvemechanism l2. In the Samuel C. Collins application Serial No. 661,253,filed April ll, 19%, there is diagrammatically shown a reversing valvemechanism suitable for the performance of the functions of the valvemechanism l2; and an example of other mechanisms suitable for thispurpose forms the subject matter of Patent No. 2,638,923, granted May19, 1953 upon an application of Win W. Paget, Serial No. 35,092, filedJune 25, 1948. The power for shifting the valve mechanism l2, to efiectconnection of the air supply conduit now with the conduit l5 and againwith the conduit i8, and connection of the conduit |3 with the conduitsH5 and I5 while the conduit H is connected with the conduits I5 and It,may be taken from any suitable source, but is desirably taken from thedrive shaft of an expansion engine [8, through any suitable reducinggearing such as that which is diagrammatically illustrated in saidCollins application, Serial No. 661,253. Reversals are adapted to beeffected at relatively short intervals; and suitable intervals may be onthe order of three minutes.

Heat exchangers 2| and 22, desirably vertically disposed, and formed asseparate units, instead of as one longer unit, in order to keep heightwithin desirable limits, are arranged in series, and entering air passesthrough the heat exchangers 2| and 22 in the order mentioned, whileleaving nitrogen passes through these same heat exchangers in the order22, 2|. Heat exchanger 2| has three courses, indicated as coaxialcourses 21A, 2|B, and HG, the first the innermost course and the lastthe outermost; and exchanger 22 has similarly relatively arrangedcourses 22A, 22B and 22C, and, outside 22C, a fourth course 22D.

Through two of the courses in series in the exchangers 2| and 22, towit, courses 2|B, 22B and courses 2|C, 22C, the entering air and theleaving nitrogen flow alternately, the entering air flowing inwardlythrough one or the other of these pairs of courses and the nitrogenflowing outwardly through the one of such pairs of courses not at anygiven moment serving for the inflow of the air. Through the thirdcourse, 2|A, of the exchanger 2| and through the corresponding course,22A, of the exchanger 22, but in the order 22A, 2|A, the leaving oxygenproduct is discharged. Exchanger 22 has, as above noted, a fourth course22D, through which a portion of the air which is entering the apparatusby way of the exchangers 2|, 22 is caused to recirculate throughexchanger 22, the better to effect the depositing out of impurities fromthe entering air stream and to increase the temperature of the airentering the expansion engine.

It has been noted, with respect to theexchangers 2| and 22, and, it willbe noted, with respect to further heat exchangers 23 and 24 hereinafterto be described, that the courses are indicated as being coaxial. Itwill, however, be appreciated that the precise form of construction ofthe exchangers is not illustrated in the diagram of Fig. 1, sincesuitable multiple-pass exchangers may assume various forms, and, in theSamuel C. Collins application above identified, a suitable form ofexchanger is illustrated, and other possible types are illustrated inLetters Patent Nos. 2,596,008 and 2,611,586, granted respectively on May6, 1952 and September 23, 1952 upon other applications of said Samuel C.Collins, respectively Serial Nos. 3,217, filed January 20, 1948 and2,877, filed January 17, 1948. Exchanger 23 will be observed shortly tobe of the four-course type, and exchanger 24 of the three-course type.

Conduit l5 communicates with course 2|B of exchanger 2|, and conduit ISwith course 2|C of exchanger 2|. The leaving oxygen product passesoutwardly through course 2|A of exchanger 2| and asses to a shop line,to a bank of cylinders, or to any other desired point or apparatus, foruse or storage, through a conduit 25. Course 2E0 of exchanger 2| isconnected by a conduit 3| with course 220 of exchanger 22. Course 2IB ofexchanger 2| is connected by a conduit 32 with course 223 of exchanger22. A conduit 33 connects course 21A of exchanger 2| with course 22A ofexchanger 22. These courses are traversed serially, in the order 22A,2|A, by the oxygen product, as later described. It will be appreciatedthat air will fiow alternately in through course 210, conduit 3| andcourse 22C or course 2|B, conduit 32 and course 223, while concurrentlynitrogen will flow outwardly through the ones of said courses andpassages last mentioned not carrying the entering air.

A suitable automatic reversing valve mechanism, generally designated4|], is provided beyond, in terms of entering air flow, the end of heatexchanger 22 last left by the entering air and first entered by theleaving nitrogen, this including four automatic check valves 4|, 42, 43and 44. This arrangement is disclosed in the Samuel 0. Collinsapplication Serial No. 661,253. The lower end of course 223 hasconnected with it a conduit 45 which leads to the check valve 4|, and abranch 46 leads from conduit 45 to check valve 42. A conduit 41 leadsfrom course 220 to check valve 44, and a branch 48 connects conduit 41,at a point between course 22C and the check valve 44, with the checkvalve 43. A conduit 49 connects the other side of check valve 43 with aconduit 50 leading fromthe check valve 4| to a suitable restrictordevice 5 l, which creates a slight difference between the pressure inthe conduit 50 and the pressure beyond the device 5!, the latterpressure being on the order of two pounds less than the pressure inconduit 50. A conduit 52 connects the conduit 50 with the bottom ofcourse 22D. A conduit 53 leads from the side of check valve 44 oppositethe conduit 47, to'the outermost course of the heat exchanger 23.Nitrogen always flows outwardly through conduit 53. A conduit 55connects the side of check valve 42 opposite the conduit 46 to theconduit 53. Each of the check valves 4!, 42, 43, and 44 opens in thedirection indicated by its and prevents opposite flow.

The restrictor 5| is connected as at 56 to a chamber '5'! within the topof an evaporatorcondenser 60 having a suitably insulated casing BI andhaving in said casing an oxygen conducting conduit or course 62 and anair conducting conduit or course 63 in close heat exchange relation witheach other. The conduit or course 53 is connected at 64 with the chamber51. The oxygen conduit or course 62 is connected by a conduit 65 withthe bottom of course 22A of exchanger 22. The top of course 22D ofexchanger 22 is connected by a conduit 66 with a conduit til-leadingfrom the chamber 51, and the reunited stream of air passes to a conduit78, which leads to the expansion engine -!8 later more fully described.

The connections of the downstream side of the restrictor 5! with thechamber 63 and with the conduit 67 have been shown as having the chamber51 common to them, but the use'of a chamber in the casing of theevaporator-condenser 68 to efiect such connections is not essential.

When the air entering the system is passing through course 223, it flowspast the check valve 6|. When course 22B is serving for outflow ofnitrogen, the nitrogen flows from conduit 53, through conduit 55 andpast check valve 42 and through conduits 46 and 45 to course 223. Whencourse 220 is serving for inflow of air, the entering air flows past thecheck valve 43. When course 220 is being used to conduct leavingnitrogen, the nitrogen flows past check valve id and through conduit H.much higher pressure than the leaving nitrogen, no check valve subjectedon its discharge side to air can be opened by the lower nitrogenpressure.

For best performance, as well during high pres sure as during lowpressure production, the arrangement of exchangers 2| and 22 hereinshown and described is preferable. It is desirable that the entering airpass upward through exchanger 2| in order that the water frozen out ofthe entering air stream, and all of which is removed in exchanger 2|,may drain by gravity'downwardly in that exchanger. Exchanger 22,however, is desirably so arranged that the at least nearly completelyliquid leaving oxygen stream which enters it during high pressure oxygenproduction shall pass upwardly therethrough. The flow of the enteringair is in opposite directions through exchangers 2i and 22 in apreferred embodiment. For low pressure oxygen production and/or withconstructions of exchanger 22 in which oxygen ilow is suitably retarded,an arrangement may be used in which the oxygen may pass downwardly inexchanger 22 as well as in exchanger 2| As the entering air is at a 6while the air passes upwardly in both of the same.

The heat exchangers 23 and 22 have been previously mentioned. Exchanger23 has four courses: a central one, 23A, a next course 23B, a thirdcourse 230, and an outer course 231151.11- rounding, as shown on thedrawings, course 230. Obviously the arrangements of the courses, and thestructure of this exchanger, are subject to wide structural variations.Exchanger 24 has a central course 24A, an outer course 246 and anintermediate course 24B. It, too, is subject to wide structuralvariation. It will be understood that the several courses willbe in goodheat exchange relation with respect to each other.

It has been noted that the conduit 531s connected with theoutermostcourse 23D of exchanger 23. This connection is with the top orsuch course. The bottom of course 23B is connected by a conduit 68 withthe bottom of course 24C of exchanger 24, and the top of course 24C isconnected by a conduit 1| with the nitrogen outlet (the efiiuxconnection) 12 or" a single column E3. The compressed air course 63 ofevaporator-condenser 62 is connected by a conduit M with the top ofcourse 2313 of exchanger 23. The bottom of said course is connected by aconduit '15 with a valve device it, which, in the particular apparatusshown, and when the latter is used for oxygen production, is adjusted toefiect a pres-. sure drop between its opposite sides on the order of 88p. s. i. for a compressor delivery pressure of p. s. i. This issubstantially the same reduction in pressure as occurs in the expansionengine later described, when the latter is operating with its longerperiod of admission, hereinafter fully explained. The downstream side ofvalve device it is connected with a conduit Ti which leads to acondenser coil or element 13 in the lower end of the column 73. Thecentral course (as shown) 23A of exchanger 23 is connected at its topwith a conduit 19 leading to the oxygen course 62 of theevaporator-condenser 60, while its bottom is connectedv with the bottomof central course 22A of exchanger 22 by a conduit Bil. A conduit 31leads from the top of the central course 24A. This is connected with thedischarge of a liquid oxygen pump, later described. The condenser unit18 isconnected at its other end (from theconduit Tl), by a conduit 82,with the intermediate course 24B of exchanger 25. The top of course 24Bis connected with a conduit 83, of which more will be shortly said.

Three of the four courses of exchanger 23 have been noted. The fourthcourse, 230, is connected at its top with an expanded air conduit 85,and its lower end is connected by a conduit 85, containing a check valve3? openable towards the conduit "ii and connected with the latter by aconnection 88. The check valve opens towards the conduit H, but onlywhen the pressure in the conduit 88 is sufficientto effect opening ofcheck valve Ell against the pressure in conduit 'l's'.

The expansion engine i8, which may be of the construction shown-in theSamuel C. Collins application, Serial No. 665,206, filed April 26, 1946,and now matured into Patent No. 2,607,322, granted August 19, 1952,provided with suitable means for predeterminedly lengthening andshortening the period of admission, or which may be of the character ofthe expansion engine employing cam follower rollers; one or'both ofwhich coact with a cam depending on whether early or late cutoff isdesired, which expansion engine is illustrated and. described in anapplication of 7 Win W. Paget, Serial No. 31,017, filed June 4, 1948,and now Patent No. 2,678,028, granted May 11, 1954, or of other suitableconstruction, includes a cylinder 90 having admission and exhaustvalves, not shown, and to the admission valve of which air underpressure is admitted from the conduit I through a conduit 9| with whichan In surge tank 92 is connected so as to minimize fluctuations in flow.A discharge or exhaust connection 93 leads from the expansion engine toa Discharge surge tank 94, which may have associated with it a strainerto catch any snow that might otherwise attain to the column while theheat exchangers 2E and 22 were not fully cooled down during the startingof the apparatus. The expansion engine supports on the top of itscylinder 9, jacketed liquid oxygen pump 95 of any suitable construction,the liquid oxygen pump being for example actuated by the expansionengine piston as is the pump shown in the last above mentionedapplication of Win W. Paget, or in any other suitable manner; and it maybe noted that the conduit BI is connected with the discharge of theliquid oxygen pump 95, while this pump has a suction connection 95leading to it from a strainer 91 which is cooled or jacketed by liquidair, the jacket herein being represented by a coil 98. To the strainer91 a conduit I00 leads from the evaporator-condenser at the bottom ofthe column 13, the conduit I00 communicating with thecondenser-unit-enclosing chamber Illl in the bottom of the column at apoint at the desired liquid oxygen level in the latter.

The Discharge surge chamber 94 has connected with it a conduit I05 whichis connected to a valve structure I06, which valve structure includes apassage or chamber I01 continuously in communication with the conduit85, and another chamber connected through a conduit I09 directly withthe interior of the column at a point spaced an appropriate distancefrom the top of the latter. The valve structure I00, which may be calleda lay-pass valve, is adapted to have the two chambers mentionedconnected in communication with each other, and thus to connect theDischarge surge chamber 94 in free communication with the upper part ofthe column through the conduit I05, valve structure I06, and conduitI09. In the drawing the constant communication between the conduits I05and 85 is indicated by the passage I01, and the communicability of thepassage or chamber I01 with the conduit I09 is indicated by the valveI08. Other constructions suited to the functions mentioned may evidentlybe used.

The expansion engine I8 is provided, in the present particularapparatus, with valve gear adapted to permit the engine to operate withadmission for a relatively short portion of its working stroke, or withadmission for a considerably longer portion of its working stroke. Aswill later be explained more in detail, when cutoff is relatively latein the working stroke to provide said long admission, the valvestructure 00 will prevent communication between the Discharge surgechamber 94 and the column through the conduit I09; and whencommunication between the Discharge surge chamber 94 and the column iseffected by the appropriate adjustment of the valve structure I06, theexpansion engine will be operated with admission for said relativelyshort portion of its working stroke.

Various means can be provided for efi'ecting the desired changes inperiod of admission, as,- for example, with a cam opened admission valveas shown in the Samuel C. Collins Patent No. 2,607,322, granted August19, 1952, the provision of selectively operable cams with differentdwells, or cams one relatively adjustable with respect to the other. Seealso for example Ferguson, 2,221,790, patented Nov. 19, 1940. Orcam-follower rollers one or both cooperating with a cam depending onwhether early or later cutoff is desired may be employed, as in theapparatus of the Paget Expansion Engine application.

Only such air will flow through the evaporatorcondenser 60 as cannotpass through the expansion engine. During -pound oxygen production,complete condensation of the fraction of air passing through the aircourse 63 of the evaporator-condenser 00 may conceivably be effected,but if more air passes through this course than can be condensed by theavailable cold provided by evaporation of liquid oxygen, at a pressureon the order of 50 p. s. i., in the course 62 of theevaporator-condenser 60, the excess unliquefied air will be condensed inevaporator-condenser 18.

The conduit 93, previously mentioned, leads to a valve device H0 whichis adapted to be adjusted to effect a reduction on the order of p. s. i.in the pressure of the fiuid (liquid air) which flows through it; andthe downstream side of the valve device H0 is connected by a conduit IIIwith the jacket 98 for the strainer 91; and the top of this jacket isconnected by a conduit H2 with a jacket N3 of the liquid oxygen pump 95,there being a conduit H0 leading from the jacket H3 to a connection H5through which liquid air may be admitted to the top of the column I3.

The column 13 may be of any suitable construction, and is illustrated asof the conventional packed type. It may obviously assume various forms,and the now abandoned Samuel C. Collins application, Serial No. 26,395,filed May 11, 1948, and the Samuel C. Collins Patent No. 2,610,046,granted September 9, 1952, show columns which are well adapted for thepurpose for which the present column is employed.

Before describing in detail the mode of operation of the apparatus shownin Fig. 1, it is desired to point out that the column may normally beoperated with a pressure on the order of 6 or 7 p. s. i., and in orderto evaporate liquid oxygen with the latent heat of condensation of airunder pressure in the condenser 18, the pressure of the air in saidcondenser should be on the order of p. s. i., and accordingly the valveH0 will be set to maintain a differential in pressure of about 60 p. s.i. between its upstream and downstream sides, the downstream side beingsubstantially at column pressure, and the upstream side substantially ata pressure of "10 p. s. i. The expansion engine, when working with thelater cutoff, has an expansion through it at least substantially equalto the difierence between 158 p. s. i., the pressure in line 70, and thepressure in the line H. Thus the expansion engine provides a pressuredrop on the order of 88 p. s. i. This 88 p. s. i. drop, plus the 70 p.s. i. pressure previously mentioned, plus the differential in pressureof about 2 p. s. 1. provided by the restrictor 5!, gives a cumulativepressure of 160 p. s. i.; and that is the pressure at which thetwo-stage compressor, not shown, which delivers air to the conduit II,may deliver air continuously. It is to be noted that the conduit I5 andvalve device'lB aresubstantially in parallel with the expansion engineandthe check valve .81, and accordingly the valve device 16 is set togive a pressure reduction on the order of 88 p. s. i., so that the airstarting at 158 p. s. i. in the chamber 5'! and passing through the aircourse 53, conduit 74, heat exchanger course 233, conduit 15 and pastvalve device it may attain to the pipe 71 at substantially the pressureat which the air is delivered through the conduit 88. Thus, it may beobserved that the sum of the column pressure, plus the reduction inpressure at the valve device l 10, plus the pressure reduction acrossthe valve device 16,

plus the 2 p. s. i. drop through the restrictor BI and plus theresistance in-various conduits also equals 160 p. s. i., thedeliverypressure of the compressor supplying compressed air to theconduit ll.

Another valuable function of passing a portion ofthe entering airthrough the evaporator-condenser resides in the fact that under varyingconditions, the expansion engine, though it may normally take a certainpercentage of the air to be processed, may at times take somewhat largerquantities; by having a substantial stream 'of air normally passingthrough the evaporatorcondenser, there is available, in the event theexpansion enginerequires more air by virtue of fortuitous changes inoperating conditions, air in the system which can be diverted andsupplied to the expansion engine and so enable the supply pressure tothe latter to be maintained constant.

The mode of operation of the described apparatus during the productionof oxygen is different, depending upon whether 50-pound oxygen or oxygensuitable for cylinder charging (say at 2000 p. s. i.) is being produced.Oxygen at either pressure may be delivered. The mode of operation forthe production of oxygen at 50 p. s. 1. pressure will be describedfirst, and then the differences when oxygen at 2000 p. s. i. is to bethe product will be explained. Following this, a pro .cedure to set theplant in operation will be described.

Air is supplied continuously, as above noted, through the conduit H at300 K. and 160 p. s.i., fromany suitable compressor. Ordinarily atwostage compressor with an aftercooler may be used as the source of airsupply.

The entering air contains water vapor and carbon dioxide. These arecaused to be sepa rated out of the air stream by cold supplied by theleaving streams of oxygen product and nitrogen. The carbon dioxide islargely deposited in the heat exchanger 22 upon the walls of the courses22B and 22C, and the Water vapor, as liquid water and as ice, in thecourse 2113 and 2IC of exchanger 2! and it may be of interest at thepresent moment to point out that the liquid oxygen drawn from thechamber HJI in the column 13 through conduit I00, the strainer 91, andconduit 95, is pumped by the liquid oxygen pump 95 through the conduitthrough the course 24A of heat exchanger 24, through the conduit 80, thecourse 23A of heat exchanger 23, conduit '19, the oxygen course 62 ofthe evaporator-condenser 60, theconduit 65, course'22A of heat exchanger22, conduit 33, and the'course 2 IA of the heat exchanger 2 I, andfinally is delivered at the -desired terminal pressure through theproduct delivery pipe 25. As has been previously pointed .out,thenitrogen leaving the column by way of 'theaconnection 12 passes throughthe conduit 1!,

through course 24C of heat exchanger 24, through conduit 68, throughcourse 23D of heat exchanger 23, through conduit 53, through one or'theother of the courses 223 or 22C of heat exchanger 22, through one or theother of the conduits 3| or 32, through one or the other of the coursesMB or ZIC of heat exchanger 2|, through one or'the other of the conduitsIE5 or it, and through the escape it, having passed through appropriatepassage means in the valve mechanism l2. Thus it will be evident thatthe streams of oxygen and nitrogen passing through the heat exchangers22 and 2! will cause the carbon dioxide and'water vapor to be condensed,or condensed and frozen, on the walls of the passages. in theseexchangers through which the entering air may at any given moment beflowing, and that liquid water will be evaporated or entrained, anddeposits of ice and carbon dioxide snow sublimed,'and be carried out, bythe leaving nitrogen stream, of the passages in which they have beendeposited. A portion of the air which is passed through the heatexchangers 2i and Z2 is caused to pass again through the heat exchanger22, through the course 22D thereof, as previously explained, flowingthrough the conduit 52, course 22D, and conduit 00 and rejoining themain mass of air which passes, during the production of low pressureoxygen, through the chamber 57 and conduit 61; and the reunited streamspass through the conduit 70 and the conduit 0! into the expansion engineto be expanded therein and to be cooled by the performance of workduring the adiabatic expansion of the fluid in the expansion engine. Theflow through conduit 52, course 22D of heat exchanger 22, and conduit 58is'caused by the device 5|, which provides approximately a 2 pounddifference in pressure at its opposite sides.

At this point it may be'noted that, regardless of the pressure of thedelivered product, some of the air supplied to the apparatus fortreatment therein always passes through the expansion engine l8, andsome of the air always passes through evaporator-condenser as, thequantity of air passing through evaporator-condenser 60 being determinedby the cutoff of the expansion engine. When the expansion engineoperates with relatively early cutoff, more air necessarily passesthrough evaporator-condenser 60. During the production of oxygen at 50p. s. i., about 12% of the total mass of entering air passes through theair course 63 of evaporator-condenser 60 in heat exchange relation withthe leaving oxygen product. When oxygen at 2000 p. s. i. is the desiredproduct, as much as 60% of all the air may pass through the air course03 of evaporator-condenser 00. The air which leaves'the heat exchanger22 on its way to pass through the chamber 5'! of evaporator-condenser 60and flow through the conduit 6! is at a temperature of K. and a pressureof p. s. 1. At the downstream side of the restrictor device 5| thepressure is 158 p. s. i. The recirculated air which flows through theconduit 50 is at a pressure of on the order of 158 p. s. i. and atemperature of K. just before it joins the fluid stream in conduit 67.When the streams have been mingled 23, and emerges at a temperature of105 K. and a pressure of 70 p. s. i., and passes the check valve 81 tomix with liquid air which has passed the valve device I5, and there isformed a stream partially of liquid. air and partially of expanded airat a temperature of 100 K. and a pressure of 70 p. s. i. It may beobserved that the air from the air course 63 of the evaporator-condenserE emerges from heat exchanger 23 and enters the conduit I at atemperature of 112 K. and a pressure of 158 p. s. i. After passingthrough the valve device I6 and undergoing a drop in pressure of about88 p. s. i., the liquid air is at the same pressure as the expanded aircoming through conduit 88.

The mixture of liquid air and expanded air at a temperature of 100 K.and a pressure of 70 p. s. i. enters the condenser coil I8 and iscondensed by reason of the giving up of heat in the process ofvaporizing oxygen in the bottom of the column. The liquid air emergingfrom the condenser I8 is at a temperature of 96 K. and a pressure of 70p. s. i., and after this liquid air has passed the valve device I I0 andhad its pressure reduced by approximately 60 p. s. i., the liquid airwill be at a temperature of 83 K. and a pressure of about 9 p. s. i.Following the jacketing of the oxygen strainer 91 and the liquid oxygenpump 85, the still liquid air will enter the top of the column at atemperature of 33 K. and v a pressure of about '7 p. s. i., and it willbe rectified therein so that substantially pure oxygen (99.5% pure, atleast) can be drawn from an appropriate point in theevaporator-condenser arranged in the bottom of the column at atemperature of 95 K. and a pressure of 7 p. s. i., or perhaps less. Thisliquid oxygen will flow through the strainer 91, conduit 06, the liquidoxygen pump 95, the conduit 8|, and the central courses, in series, ofheat exchanger 24, heat exchanger 23, evaporator-condenser 60, heatexchanger 22, and heat exchanger 2|, and emerge, when 50-pound oxygen isbeing produced, in the form of gaseous oxygen at the mouth of theproduct pipe 25.

When oxygen for cylinder charging is to be produced, the valve structureI05 will be operated to connect the conduits I05 and I09 and theexpanded air leaving the expansion engine will then pass through theconduit I05, the valve structure I06, and the conduit I09 into thecolumn, and the pressure of the air in the conduit I05 will be reducedsubstantially to that within the column, and accordingly no moreexpanded air will be discharged through the check valve 0?, because thisvalve will be held closed by the pressure, on the order of 70 p. s. i.,which subsists in the conduit ll. At the time the valve structure I06 isoperated to permit the exhaust from the expansion engine to passsubstantially directly into the column through the conduit I09, thepoint of cutofiof the expansion engine I8 will be changed to make itmuch earlier in the stroke; and, the speed of the expansion engineremaining unaltered, much lessroughly half as muchair can go through theexpansion engine. As a result of this, the air which cannot flow throughthe conduit 61 and be passed through the expansion engine will ofnecessity go through the air course 63 of evaporator-condenser 60, and,having passed through course 233 of heat exchanger 23, this now muchlarger mass of air, perhaps 60% of the total mass, will pass through thevalve device It and enter the condenser coil I8 of theevaporator-condenser at the bottom oi the column I3 and be liquefiedtherein. This larger volume could not be liquefied in theevaporator-condenser 00 and the heat exchanger 23 because the oxygen nowat a much higher pressure cannot be vaporized at the temperature ofcondensing air. The reduced volume of liquid air from condenser coil I8will pass through the heat exchanger 24 by way of course 243 and nextpass through conduit 83 and the valve device I I0 and then, afterjacketing the strainer 91 and the liquid oxygen pump 95, will be passedinto the top of the column for rectification. A much smaller percentageof the total oxygen content of the air entering the apparatus will bedelivered during the production of ZOOO-pound oxygen than during theproduction of 50-pound oxygen.

In starting up the apparatus, the valve I08 will be open and for aconsiderable period, on the order of two hours, and the expansion enginewill be operated with relatively late cutofi. This will mean that mostof the air will pass through the expansion engine, a desirable thing atthis time because there would be no oxygen to efiect condensation of airin evaporator-condenser 60. The entering air through whichever coursesof heat exchangers 2i and 22 it may pass, will, about 12% of it, flowthrough the evaporator-condenser 50, heat exchanger 23, valve device I0,condensing unit I8, exchanger 24, conduit 83, and past the valve deviceIIIl through the jacket for the oxygen strainer 91, the jacket II3 forthe liquid oxygen pump 95, and then-through the conduit H4 andconnection II5 into the top of the column I3. During a considerableportion of the starting operation-the cooling down periodthis air willsimply flow out through the conduit 7 I, etc. and be discharged. Therelatively large amount, about 88%, of the air which passes through theexpansion engine I8 will pass into the column through the conduit I09,and it too will discharge through the conduit II to the atmosphere. Asthe unit cools down, a little liquid will commence to form, and as soonas this stage is reached, the expansion engine will be shifted to earlycutoiT, thus increasing the refrigeration, and for another period,perhaps an hour, the exhaust from the expansion engine will stillcontinue to be discharged through the connection I09 into the column.When the liquid finally builds up high enough so that oxygen can bedrawn through the conduit I00, the apparatus will be all ready to go toZOOO-pound oxygen production, or, by closing the valve I08 and makingthe point of cutoff in the expansion engine much later, 50-pound oxygencan be produced. It will be noted that during the later stages of thecooling down operations, the bypass valve I08 will still be open and theexpansion engine will be working with an early cutoii, and that when theliquid level in the column reaches the overflow point, the machine willbe ready to fill cylinders, but if 50-pound oxygen be desired, thebypass valve can be closed and the valve gear arranged in the expansionengine for late cutofi.

Certain points not previously mentioned, or perhaps deservingreemphasizing, may be noted now with respect to the embodiment of theinvention, from its apparatus aspect, which has so far been described.The motion of the recirculating air flowing through the conduit 52 iscounterflow relative to the entering air stream, and, as previouslyobserved, it is caused to take place by providing a slightly lessresistance to flow thrDugh the course 22D of heat exchanger 22 than toflow past the device and through the chamber 5'! of evaporator-condenser60.

As a portion-a minimum of about 12%of the entering air always passesduring normal operation through the evaporator-condenser 60 inheatexchange relation with the iiuid flowing through the oxygen productline, there will always, as soon as low enough temperatures areattained, be some liquid passing into the top of the column.

During the cooling down period, and also when oxygen at 2000 p. s. i. isthe desired product, the expanded air may enter the column through thevalve controlled connection 09 at a point perhaps three-quarters of theway up the column, instead of having to pass around through heatexchanger 23, the conduit 80 and the check valve 87. Indeed, no air canthen pass through the circuit last mentioned, because the air in theconduit Tl will be at a pressure so much greater than the pressure inconduit 85, as to maintain the check valve closed.

During the production of 50-pound oxygen, the main fiow or" expanded air(about 88% of the total enteringair) passes into the top of course 230of heat exchanger 23 and passes down through this heat exchanger in heatexchange relation both with liquid oxygen produced in the system andwith the leaving nitrogen stream. The expanded air, at 105 K. and '70 p.s. i. pressure-the same pressure as at release from the expansionengine-then passes through the oneway check valve 8? and enters thecondenser unit -18 in the bottom of the column, and the expanded air iscondensed, its latent heat of condensation serving to evaporate liquidoxygen at a lower pressure in the bottom of the column. The liquefiedair goes into the bottom of heat exchanger 24 and gives up some of itsheat to the nitrogen and to the liquid oxygen which also flow throughexchanger 24, and then passes through the valve device H0, which causesa reduction in pressure on the order of 60 p. s. i., this resulting in afurther cooling of the liquid air and some vaporization. After passingaround the liquid oxygen filter which it jackets, the liquid air isused, as will be recalled, to jacket the liquid oxygen pump also, and itthen enters the top of the column at a temperature of 83 K. and at apressure of on the order of 7 p. s. i. The process of rectification inthe column results in there being available liquid oxygen in theevaporatorcondenser at the bottom of the column, specifically in thechamber Hill surrounding the condenser unit 18, at a temperature ofabout 95 K. and a pressure of around 7 p. s. i., while nitrogen, withthe single column rectifier, containing from '7 to oxygen, and at atemperature of 83 K. and a pressure of 7 p. s. i., passes out of the topof the column. The liquid oxygen is filtered as it passes to the liquidoxygen pump and is forced by the latter at a pressure commensurate withthe desired product pressure successively through heat exchanger 20,heat exchanger 23, evaporator-condenser 00, heat exchanger 22, and heatexchanger 2! to the point of product delivery, absorbing from theentering air stream the heat necessary to vaporize it, when 50-pcundoxygen is being produced, while passing through evaporator-condenser 60,and the absorbed heat resulting in a change of state or" the enteringair from gaseous to liquid form. When 2000-pound oxygen is beingproduced, the liquid oxygen cannot be evaporated in theevaporator-condenser'til and so there is simply a temperatureincrease-of a few degrees in the oxygenpassing throughevaporator-condenser 60, the evaporator-condenser 60 then operatingsimply as a heat exchanger. Nevertheless, when oxygen at 2000 p. s. i.pressure reaches the cylinders to which product line 25 may beconnected, this oxygen is in a vapor state. The valve devices 76 and H0will be adjusted as necessary to effect the desired operatingcharacteristics at all times and at whatever product pressure.

During the production of -pound oxygen, the portion of the air thatsplits off from the main stream in the header of evaporator-condenser00-an amount which may be 12% of the whole during normal 50-pound oxygenproductionis largely condensed in evaporator-condenser and any excessthat may pass through the evaporator-condenser 60 without liquefactionwill be liquefied in the evaporator coil iii. If 2000-pound oxygen isthe product, no expanded air enters the evaporator-condenser 8 with theair going by way of exchanger 23 from the evaporatorcondenser 60, as thelow pressure of the expanded airthis air has been expanded through amuch greater range of expansion when the expansion engine is workingwith early cutoff'will not permit it to effect opening'of the checkvalve 87 even though the exhaust from the expansion engine communicatesfreely with the check valve 81. Note that the exhaust from the expansionengine communicates freely through the conduit itii with the column atthis time. The larger quantity of air going through theevaporatorcondenser '53 and heat exchanger 23 and entering the condenser'58, even though little of it may have been condensed before the arrivalat the condenser 78, is at a pressure of p. s. i. suited forcondensation .by the latent heat of evaporation of oxygen which isvaporized in the chamber iili. The total quantity of oxygen producedwhen 2000-pound oxygen is being supplied will be proportionately muchless than when 50 pound oxygen is the end product. It may be noted thatthe exhaust pressure of the expansion engine during the production of2000-pound oxygen will be essentially the same as column pressure,namely 7 p. s. i.

Roughly, during cylinder charging (2000-pound production) 40% of the airgoes through the expansion engine and directly into the column, whilethe other 60% follows the course normally taken during 50-pound oxygenproduction by but 12% of the air supply to the apparatus. This change inthe air flow distribution is due to the much earlier cutoff which occursduring 2000- pound oxygen production. It will be understood that theexpansion engine operates at a predetermined speed, that the quantity offluid which can pass through it is accordingly determined by the pointof cutoff, and that, accordingly, with late cutoff, a much largerpercentage of the total entering air stream can pass through theexpansion engine than when cutoff is made early.

With an apparatus having, during low pressure oxygen production, thetemperatures and pressures above mentioned, the relatively later cutoffof the expansion engine would theoretically take place at about 70%ofthe working stroke; and during high pressure oxygen production therelatively early cutoff would be at theoretically on' the order of 25%of the working stroke, but these percentages are only illustrative. Forexample, there are two factors which in practice would tend to call forlater cut-off in both modes of operation, namely, that it is desirablein practice to handle at least a little larger than the theoretical massof air to insure adequate refrigeration, and, moreover, with actualapparatus, the expected temperatures and pressures are not alwaysattained.

By sending the expanded air through the top three or four trays of thecolumn, the liquid air flowing downward can be caused to wash a fractionof the oxygen from the expanded air.

During the production of 50-pound oxygen, the percentage of oxygen inthe waste gas leaving the top of the column is approximately andtheoretically might be as low as 7%. The percentage of oxygen in theliquid air which is fed into the top of the column is approximately 21%.The percentage of oxygen in the liquid which is in equilibrium withgaseous air of 21% oxygen is approximately 47%. As long as descendingliquid has less than 47% oxygen in it, it can extract some oxygen fromair passing directly into the column.

Refrigeration is obtained from the Joule- Thomson efiect, and from theoperation of the expansion engine. The Joule-Thomson effect givesapproximately 2 K. of cooling. During normal 50-pound production, 12 K.of cooling is obtained from the expansion engine. When filling cylinders(producing oxygen at 2000 p. s. i.), the expansion engine provides 42 K.of cooling of theair which passes through it, but only 40% of the totalair stream passes through the expansion engine. The 2 K. of coolingobtained by the Joule-Thomson effect as well as the 12 K. coolingobtained from the expansion engine applies to the flowing stream ofentering air.

The nitrogen, as above noted, was at 83 K., and a pressure of 7 p. s. i.in conduit II. In conduit 53 it is at 109 K. and 5 p. s. i. Between theexchangers 22 and 2| it is at 176 K. and 3 p. s. i. The leaving oxygenproduct is at 178 K. between the heat exchangers 22 and 2i, and in theconduit 65 is at 110 K. The entering air between heat exchangers 2| and22 is at 184 K. and 160 p. s. i. All pressures and temperatures are, ofcourse, approximate.

In Fig. 1 an embodiment of the invention from its apparatus aspect isdisclosed in which a single column is used. The invention may also beembodied in its apparatus aspect in an oxygen generator employing adouble column,

and the method aspect of the invention may be practiced with such anapparatus. Fig. 2 discloses an oxygen generator in accordance with theinvention and incorporating a double column I29. Much of the structureof Fig. 2 corresponds to that of Fig. l, and the principal differencesreside in the utilization of the double column and the changes whichthat makes necessary.

The column I includes a high pressure chamber or section I2! and a lowpressure chamber or section I22, and these are separated by a partitionwall I23 which is provided with a plurality of depending heat exchangeelements I24 open at their ends communicating with the chamber I22 andclosed at their bottom ends !25. An inclined annular wall I26 projectsinwardly at the top of the high pressure chamber I2I and underlies asubstantial number of the depending heat exchange elements I24. Theconduit 11 in Fig. 2 bears the same relation to the check valve 81 andto the valve device 16 which it bears in Fig. 1, but it communicates atI28 with the high pressure chamber I2I of the double column, near thebottom of that chamber. Ac-

cordingly, liquid air and expanded air pass into the bottom of the highpressure chamber I2I in a united stream. When the apparatus is operating to produce oxygen, substantially pure nitrogen (about 98% pure)drips from the heat exchanger elements I24, and a portion of it iscollected in an annular trough I29 which is formed between the annularsloping wall I26 and the outer wall of the column. From this trough I29a conduit I30 conducts the liquid nitrogen to a heat exchanger 24 (afour-course one), and the nearly pure nitrogen passes through the course24'C of this heat exchanger and then passes through a conduit I32 and avalve device H0, and from the latter through a conduit I33 to a coolingcoil or jacket I34 surrounding the strainer 91 for liquid oxygen. Thecooling coil i34 is connected in series with a jacket II3 for the liquidoxygen pump, and from this jacket a conduit I I4 leads to a connectingdevice I36 arranged in the top of the columns low pressure chamber I22.From the bottom of the high pressure chamber I2I of the double columnI20, a conduit I40 leads to the course 24'B of heat exchanger 24', andfrom this course the enriched air which is formed in the chamber I2I bya process of partial rectification therein is delivered through aconduit MI to a valve device III)" whose other side is connected by aconduit I42 with the connection I43 leading from a conduit I44 connectedwith the Discharge surge chamber 94 and also connected through thecasing of a bypass valve structure I 06' with a conduit I45 which isconnected with the course 23C of the heat exchanger '23. The other endof the course 230 is connected with the conduit 86 which leads to thecheck valve 81 and to the conduit 88 which communicates with the conduit11 at a point in the latter just beyond the valve device IS. The liquidoxygen pump 95 takes liquid oxygen from the chamber I22 via a conduit Iand the strainer 91 and discharges it through a conduit BI into the topof course 24A of heat exchanger 24' and a conduit 80, the course 23A ofheat exchanger 23', conduit I9, oxygen course 62 of evaporator-condenser80, conduit 85, course 22A of heat exchanger 22, conduit 33, and course2IA of heat exchanger 2i, delivering the oxygen pumped by the oxygenpump 95 to the delivery conduit 25.

The mode of operation of this apparatus differs from that of the firstembodiment of the invention described essentially only in particularswhich grow out of the employment of a double column instead of a singlecolumn. The valve devices I I0 and H3" each control the flow of one ofthe fluids which originated in the high pressure chamber I2I of thedouble column. They are therefore quite similar in construction andeffect like reductions of pressure, herein approximately '75 p. s. i.One of them has the fluid passing from its downstream side into the lowpressure chamber I22 of the double column at a point somewhat lower inthat chamber than the other, as will be noted. The nearly pure nitrogenpasses through the conduit I36, through course 24C of heat exchanger24', through conduit I32, through valve device IID', conduit I33,cooling coil I34, jacket H3, conduit II4, and through the connection I36into the top of the upper section of the double column. The enriched airpasses through the conduit I40, course 24B of exchanger 24, conduit I4I,valve device IIO, conduit I42, and conduit I43 into the chamber I22.

Rectification takes place in the manner common to double columns inthetwo compartments of column i 20. That nitrogen is nearly pure (98%) byreason of the rectification process which goes on in chamber l-2l hasbeen mentioned. Enriched air that leaves the bottom of the chamber I 2!contains from 40 to 50% oxygen. The pressure in the lower section l2!may be between 75 and 85 p. s. i.; the pressure in the upper section I22 from 5 to 10 p. s. i. The pure oxygen drawn off from the bottom ofchamber I22 may desirably be pumped at a pressure of approximately 50 p.s. i. through course ZQ'A of exchanger 24', conduit 80, course 23'A ofexchanger 23', and conduit 79 into the oxygen course 62 ofevaporator-condenser 60. At this pressure the saturation temperature ofthe oxygen will be just a little below the saturation temperature of theinfiowing air, at 158 p. s. i. Accordingly there will be, with thequantity of compressed air which fiows during low pressure, 50-poundoxygen production, to wit, 12% of the whole, vaporization of the leavingoxygen and at least substantially complete liquefaction of the air whichpasses through the evaporator-condenser 60. However, if completeliquefaction of this air does not occur, such liquefaction will takeplace in the high pressure chamber 12! of the double column.

Inthis form of the invention as well as in the form previouslydescribed, it will be clear that the pressure drop inthe expansionengine and the pressure drop caused by the valve device H, the pressuredropat the restrictor and the pressure in the chamber I22 of the columncumulatively amount to the pressure at which air issupplied to thesystem from the compressor. Likewise, in the parallel connection, therestrictor 5 i with its 2 p. s. i. pressure drop, the valve device 16with its 88 p. s. i. pressure drop, the valve H ll" with its 60' p.s. 1. pressure drop, and the pressure in the low pressure chamber I22cumulatively equal the supply pressure.

It will be clear from what has been said that in the second form of theinvention, as well as in the first, there is conservation ofrefrigeration in a highly desirable manner. As above noted, compressedair at 160- p. s. i. maybe condensed when the temperature is reduced tosay 112 K. when. brought into heat transfer relation with liquid oxygenat a pressure of 50 p. s. i. and a temperature of 107 K. By pumping theliquid oxygen from the column and increasing its pressure to. the valuegiven, and bringing it into heat transfer relation with the entering airin the evaporator-condenser 69, about 12% of the enteringair can beliquefied, and during normal 50'-pound oxygen production, the periods ofadmission of the expansion engine may be so predetermined that 'justabout 12% of the entering air will not be capable of passing through theexpansion engine and will be caused to flow through evaporator-condenser60. If all this air is not'liquefied in this evaporator-condenser, thiswill do no harm because the air will be condensed in theevaporator-condenser at the bottom of the-column, in the single columnapparatus, and no harm will be done in the double column apparatuseither. If an oxygen product at an excess of 50 p. s. i. were desiredbut in gaseous form,a. much smaller oxygen compressor would be requiredwith the use of my invention than if the initial pressurization were noteffected on the liquid oxygen. Appropriate va-lve' device adjustmentswillbe madeas necessary whether the 18 occasion therefor be fluctuatingconditions or changes in product pressure.

In both illustrated apparatuses it will be understood that arrangementsare provided in which there is a substantial economy both ofrefrigeration and power through the evaporation of liquid oxygen placedunder a pressure above column pressure by a relatively smalldisplacement pump, which evaporation is effected by heat given up by afraction of the entering air when the same is condensed by therefrigeration provided by the vaporization of the liquid oxygen and thisis also true of the improved method. Other features and advantages ofthe systems have been pointed out above or will be apparent from Whathas already been said, and require no repetition here.

It is to be understood throughout the foregoing specification thatpressures and temperatures are approximate in some cases, and that,moreover, pressure drops due to friction in pipes have generally goneunmentioned.

This application is a division of my application Serial No. 122,077,filed October 18, 1949, now abandoned, and a continuation-in-part of mycopending applications, Serial No. 30,388, filed June 1, 1948, andSerial No. 81,589, filed March 15, 1949, both of which are also nowabandoned.

While there are in this application specifically described two formswhich the invention may assume in practice, and two illustrativeapplications of the improved method from its various aspects, it will beunderstood that these have been disclosed for purposes of illustrationand that the invention from both of its major aspects may be modifiedand. embodied in various other forms and practices without departingfrom its spirit or the scope of the appended claims.

What is claimed is:

1. Method of producing substantially pure gaseous oxygen from air whichincludes passing air in continuous flow through at least one heatexchanger, an expansion engine, another heat exchanger, the boiler of afractionating column, still another heat exchanger and the rectifyingportion of a column in series, simultaneously passing efiluent nitrogenfrom the column through the heat exchangers in a direction of flowreverse to that of the air in said exchangers, and passing oxygen fromthe column through each of said exchangers also in counterflow relationto the air flow therein.

2. Method of producing substantially pure gaseous oxygen from air whichincludes passing air in continuous flow through at least one heatexchanger, an expansion engine, another heat exchanger, the boiler of afractionating column, still another heat exchanger and the rectifyingportion of a column in series, simultaneously passing the effluentnitrogen from the column through the heat exchangers in reverse orderand in a direction of flow reverse to that of the air in saidexchangers, and passing oxygen from the column through each of saidexchangers also in reverse order to the air and in counterfiow relationto the air flow therein.

3. Method of producing substantially pure gaseous oxygen from compressedair which includes the moving, through an evaporator-condenser, a heatexchanger, and a valve device, into a column, of a quantity of air inheat exchange relation, in said evaporator-condenser and said heatexchanger, with liquid oxygen from the column but at higher than columnpressure, said air and oxygen each the sole fluid stream in heatexchange relation with the other in said evaporator-condenser, and sopredetermining the pressure and mass of the air that there may besuificient liquefaction thereof to effect by the heat given up therebyin liquefaction vaporization of the total quantity of oxygen produced inthe column.

4. Method of producing oxygen at super-column pressure with theconservation of refrigeration and minimization of power input whichincludes the rectification of oxygen in column, the imposition ofpressure upon liquid oxygen taken from the column to bring it to adesired super-column pressure, the passage of the oxygen product soincreased in pressure through an evaporator-condenser, and causing sucha portion, less than the whole, of the air processed to produce theoxygen to pass through such evaporator-condenser in heat exchangerelation therein only with the oxygen product, and at such a pressure asto evaporate, by its own heat of condensation, the oxygen product.

5. Method of producing from air substantially pure oxygen gas at adesired pressure above column pressure which comprises passing air insuccession through at least one heat exchanger, an expansion engine,another heat exchanger, the boiler of a fractionating column, a furtherheat exchanger, and through a valve device, into the top of afractionating column wherein the air is separated into oxygen and aneilluent, and simultaneously passing this efliuent in re verse directionof flow through the heat exchangers in the reverse order of their firstmention, and simultaneously delivering liquid oxygen from said columnthrough a pump capable of imposing the desired pressure thereon and thenpassing the oxygen through the heat exchangers in the same order as theefiluent and through an evaporator-condenser arranged between a pair ofsaid heat exchangers, to cause the oxygen to be delivered in a gaseousstate and at substantially ambient temperature but at the desiredpressure, the efiiuent being delivered at substantially atmosphericpressure.

6. Method of producing from air substantially pure oxygen gas at adesired pressure above column pressure which comprises passing air insuccession through at least one heat exchanger, an expansion engine,another heat exchanger, the boiler of a fractionating column, a furtherheat exchanger, and through a valve device into the top of afractionating column wherein the air is separated into oxygen andefiiuent, and simultaneously passing this eiiluent in reverse directionof flow through the heat exchangers in the reverse order of their firstmention, and simultaneously delivering liquid oxygen from said columnthrough a pump capable of imposing the desired pressure thereon and thenpassing the oxygen through the heat exchangers in the same order as theeffluent and through an evaporatorcondenser arranged between a pair ofsaid heat exchangers, to cause the oxygen to be delivered in a gaseousstate and at substantially ambient temperature but at the desiredpressure, the efiluent being delivered at substantially atmosphericpressure and at substantially ambient temperature.

7. Method of producing oxygen at super-column pressure, withconservation of refrigeration and minimization of power input, whichincludes passing air through at least one heat exchanger, dividing theair, passing a portion of the air through an expansion engine,liquefying the air exhausted from the expansion engine and passing itthrough a column, passing another portion of said air through anevaporator-condenser, passing said second portion through the column,withdrawing liquid oxygen from the column and imposing on it a pressurein excess of the pressure in the column, and passing the liquid oxygenthrough said evaporator-condenser and said heat exchanger, said air andoxygen being the only fluids in heat exchange with each other in saidevaporator-condenser, and predetermining the pressures of the air andoxygen as they pass through said evaporator-condenser, and theproportion of the air passing through said evaporator-condenser, toeffect at least partial liquefaction of the air in saidevaporator-condenser and vaporization of the oxygen in saidevaporatorcondenser.

8. Means for producing substantially pure oxygen at low pressure fromair at room temperature and at a pressure on the order of pounds persquare inch, which comprises a heat exchanger, an expansion engine,conduit means for leading said compressed air into said heat exchanger,conduit means for leading said compressed air from said heat exchangerto said engine, a second heat exchanger, conduit means for leadingexpanded gas from the exhaust outlet of said engine to said second heatexchanger, a fractionating column having a boiler through which the airfrom said second heat exchanger flows, and a third heat exchangerconnected with said boiler, said column also having an outlet foroxygen, the said exchangers, engine and boiler being so arranged thatair passes through them in series, the top of said fractionating columnand said outlet for oxygen being connected with the third heatexchanger, and the three said heat exchangers being connected with oneanother so that the eiiluent from said fractionating column and theoxygen pass into and through said third, second and first heatexchangers in that order and in a reverse direction of flow from that ofsaid air.

9. The method of producing, by the separation of compressed air, bycooling and rectification, oxygen at pressures above column pressure,with maximum conservation of refrigeration, including passing compressedair through at least one heat exchanger, dividing the air, passing aportion thereof through an expansion engine and through a column,passing another portion thereof through an evaporator-condenser andthrough a column, withdrawing liquid oxygen from the column and pumpingit at a pressure higher than the pressure within the column through theevaporator-condenser in heat exchange relation therein only with the airportion passing through the latter, and utilizing in theevaporator-condenser the cold of the oxygen to absorb latent heat ofcondensation from said air portion.

10. The method of separating the constituents of a gaseous mixture toobtain as an end product one of its constituents in substantially pureform, which method includes expanding one portion of a compressedgaseous mixture with the production of external work, subjecting anotherportion of the compressed gaseous mixture to heat interchange with theend product in isolation from the efliuent, subjecting both of saidportions to heat interchange with said end product and the efliuentwhile said portions remain separated from each other, reducing thepressure of said second portion to the pressure of the first portion,combining said portions and liquefying the mixture through heatinterchange with a body of liquefied gas, reducing the pressure of theliquefied mixture, and subjecting the mixture to rectification to formsaid'body of liquefied gas.

11. The method of separating the constituents of a gaseous mixture toobtain as an end product one of its constituents in substantially pureform, which method includes expanding one portion of a compressed gaseoumixture with the production of external work, subjecting another portionof the compressed gaseous mixture to heat interchange with the endproduct alone, subjecting both of said portions to heat interchange withsaid end product and the effluent while said portions remain separatedfrom each other, reducing the pressure of said second portion to thepressure of the first portion, combining said portions and liquefyingthe mixture through heat interchange with a body of liquefied gas,subjecting said liquefied mixture to heat interchange with the endproduct, reducing the pressure of the liquefied mixture, and subjectingthe mixture to rectification to form said body of liquefied gas. 12. Themethod of separating the constituents of a gaseous mixture to obtain asan end product one of its constituents in substantially pure form, whichmethod includes expanding one portion of a compressed gaseous mixturewith the production of external work, subjecting another portion of thecompressed gaseous mixture to heat interchange with the end productseparately, subjecting both of said portions to heat interchange withsaid end product and the effluent while said portions remain separatedfrom each other, reducing the pressure of said second portion to thepressure of the first portion, combining said portions and liquefyingthe mixture through heat interchange with a body of liquefied endproduct, reducing the pressure of the liquefied mixture, and subjectingthe mixture to rectification to form said body of liquefied gas. 13. Themethod of separating the constituents of a gaseous mixture to obtain asan end product one of its constituents in substantially pure form byexpanding one portion of a compressed gaseous mixture with theproduction of external Work, subjecting another portion of compressedgaseous mixture to heat exchange with the end product in isolationfromthe effluent, subjecting both of said portions to heat exchange with theend product and the effluent while said portions remain separated fromeach other, reducing the pressure of the second portion to the pressureof the first portion, combiningv said portions and liquef-ying themixture through heat interchange with a body of liquid gas, subjectingthe liquefied mixture to heat exchange with the end product and theefiiuent, reducing the pressure of the liquefied mixture and subjectingthe mixture to rectification to form said body of liquefied gas, whichmethod includes withdrawing the end product in liquid form from therectifier, increasing its pressure to the pressure desired for use, anddetermining the portion of the compressed gaseous mixture which is to besubjected to heat exchange with said end product so that the latent heatof condensation thereof shall be at least equal to the latent heat ofevaporation of said end product at said pressure of use.

.14. The method of separating the constituents of a gaseous mixture toobtain as an end product one of its constituents in substantially pureform by expanding one portion of a compressed gaseous mixture with theproduction of external work,'subjecting another portion of compressedgaseous mixture to heat exchange with the end product alone, subjectingboth of said portions to heat exchange with the end product and theefiiuent while said portions remain separated from each other, reducingthe pressure of the second portion to the pressure of the first portion,combining said portions and liquefying the mixture through heatinterchange with a body of liquid gas, subjecting the liquefied mixtureto heat exchange with the end product and the effluent, reducing thepressure of the liquified mixture and subjecting the mixture torectification to form said body of liquefied gas, which method includeswithdrawing the end product in liquid form from the rectifier,increasing its pressure to the pressure desired for use, and determiningthrough the capacity of the expansion engine the portion of thecompressed gaseous mixture which is to be subjected to heat exchangewith said end product so that the latent heat of condensation thereofshall be at least equal to the latent heat of evaporation of said endproduct at said pressure of use.

15. The method of separating the constituents of a gaseous mixture toobtain as an end product one of its constituents in substantially pureform and delivering said end product under a pressure above its pressureupon separation from the mixture, which method includes expanding oneportion of a compressed gaseous mixture with the production of externalwork, subjecting another portion of the compressed gaseous mixture toheat interchange with the end product separately, subjecting both ofsaid portions to heat interchange with said end product and the efiluentwhile said portions remain separated from each other, reducing thepressure of said second portion to the pressure of the first portion,combining said portions and liqueiying the mixture through heatinterchange with a body of the end product in the liquid state, reducingthe pressure of the liquefied mixture, subjecting the mixture torectification to form said body of end product in the liquid state, andpositively pumping said endproduct from said body at the desireddelivery pressure, utilizing the liquefied mixture at its reducedpressure to maintain the liquefied end product below its boiling pointand thereby prevent vapor lock interference with the pumping.

1c. The method of producing, by the separation of compressed .air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingthe compressed air through at least one heat exchanger, dividing theair, passing a portion thereof through an expansion engine, passinganother portion thereof through an evaporator-condenser in heat exchangerelation in the latter only with oxygen product, uniting and liquefyingsaid portions, reducing the pressure of the liquefied air and rectifyingit in a column, withdrawing liquid oxygen from the column and pumping itat a pressure above column pressure through the evaporator-condenser inheat exchange relation with the air passing through the latter andutilining in said evaporator-condenser the refrigerative effect or" theevaporating liquid oxygen at its pressure substantially above columnpressure to liqueiy air passing through said evaporatorcondenser.

17. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures. above atmospheric,

with maximum. conservation of refrigeration, in-

eluding passing the compressed air through at least one heat exchanger,dividing the air, passing a portion thereof through an expansion engine,passing another portion thereof through an evaporator-condenser in heatexchange relation in the latter with oxygen product only, combining andliquefying said portions, reducing the pressure of the liquefied air andrectifying it in a column, withdrawing liquid oxygen from the column,and pumping it through the evaporatorcondenser in heat exchange relationwith the air portion passing through the latter, utilizing in saidevaporator-condenser the refrigerative effect of evaporating liquidoxygen to liqueiy substantially the entire portion of air passingthrough said evaporator-condenser.

18. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above atmospheric, withmaximum conservation of refrigeration, including passing the compressedair through at least one heat exchanger, dividing the air, passing aportion thereof through an expansion engine, passing another portionthereof through an evaporator-condenser, combining said portions andliquefying the same, reducing the pressure of the liquefied air andrectifying it in a column, withdrawing liquid oxygen from the column andpumping it, at a pressure higher than the pressure within the rectifier,through the evaporatorcondenser in heat exchange relation therein onlywith the air passing through the latter and utilizing in the latter theheat of condensation of the air to vaporize in said evaporator-condenserthe oxygen at its pressure substantially above rectifier pressure.

19. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingthe compressed air through at least one heat exchanger, dividing theair, passing a portion thereof through an expansion engine, passinganother portion thereof through an evaporator-condenser, combining saidportions and liquefying the same, reducing the pressure of the liquefiedair and rectifying it in a column, withdrawing liquid oxygen from thecolumn and pumping it, at a pressure higher than the pressure within therectifier, through the evaporator-condenser in heat exchange relationtherein only with the air passing through the latter and utilizing inthe latter at least a portion of the heat of condensation of the air tovaporize the oxygen at its pressure substantially above rectifierpressure.

20. The method of producing oxygen at pressures above atmospheric withmaximum conservation of refrigeration including passing compressed airat a pressure on the order of 160 p. s. i. through at least one heatexchanger, dividing the air, passing a portion thereof through anexpansion engine, passing another portion thereof through anevaporator-condenser, combining said portions and lique'fying the same,reducing the pressure of the liquefied air and rectifying it in acolumn, withdrawing liquid oxygen from the column and pumping it at apressure on the order of 50 p. s. i. through the evaporator-condenser,utilizing in the latter the heat of vaporization of the oxygen at saidpressure on the order of 50 p. s. i. to liqueiy at least the majorportion of air passing through said evaporator-condenser, and passingthe vaporized oxygen through said at least one heat exchanger toconserve the refrigeration it possessed, on leaving theevaporator-condenser, by cooling the entering compressed air.

21. The method of producing oxygen with maximum conservation ofrefrigeration including passing compressed air at a predeterminedpressure through at least one heat exchanger, dividing the air, passinga portion thereof through an expansion engine, passing another portionthereof through an evaporator-condenser, liquefying said portions,reducing the pressure of the liquefied air and rectifying it in acolumn, withdrawing liquid oxygen from the column and pumping it, at atleast close to the maximum pressure at which it is vaporizable by thelatent heat of condensation of the compressed air at the pressure underwhich the latter is fed to the evaporator-condenser, through theevaporator-condenser in heat exchange relation therein with thecompressed air alone, to liquefy at least a portion of the air passingthrough the evaporator-condenser by the refrigeration of the evaporatingoxygen.

22. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, and expansion engine, a column, aliquid oxygen pump, means for connecting said at least one heatexchanger to deliver air under pressure in divided streams to saidevaporator-condenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the base of said column,means including an adjustable valve device for delivering air from saidevaporator-condenser to the base of the column at the same pressure asthe exhaust from the expansion engine, means for connecting said liquidoxygen pump with said column at a point at the normal liquid oxygenlevel therein, and means for conducting the discharge from said liquidoxygen pump to said evaporator-condenser.

23. In an apparatus for the separation of gases by the liquefaction andrectification of a mixture thereof, in combination, at least one heatexchanger, an evaporator-condenser, an expansion engine, a column, aliquid oxygen pump, means for connecting said at least one heatexchanger to deliver air under pressure in divided streams to saidevaporator-condenser and to said expansion engine, means for deliveringair exhausted from said expansion engine to the base of said column,means including a valve device for delivering air from saidevaporator-condenser to the base of the column at the same pressure asthe exhaust from the expansion engine, means including a valve devicefor delivering the air of both streams to a higher point in said column,means for connecting said liquid oxygen pump with said column at a pointat the normal liquid oxygen level therein, and means for conducting thedischarge from said liquid oxygen pump to said evaporator-condensen 24.In apparatus for producing and delivering oxygen gas under pressuressubstantially in excess of that under which the oxygen is separated, thecombination of an expansion engine by which a. portion of a compressedgas mixture including oxygen is cooled by expansion with the performanceof Work, a two-course evaporator-condense in which another portion ofthe compressed gas is liquefied by traveling in proximity to out-goingoxygen, a rectification column in which any of the compressed gasmixture not previously liquefied is liquefied and the oxygen isseparated, a connection with the column from which liquid oxygen may bedrawn, and a liquid oxygen pump having its suction connected with saidconnection and its discharge leading to said evaporator-condenserwhereby liquid oxygen is supplied to the latter, the pressure of thecompressed gas mixture and the mass thereof passing through saidevaporator-condenser being such as to evaporate completely the outgoingYgen product.

25. In apparatus for producing and delivering oxygen gas under pressuressubstantially in excess of those under which the oxygen is separated,the combination of an expansion engine b which compressed air is cooledby expansion with the performance of Work, an evaporatorcondenser inwhich other compressed air is liquefied by heat exchange with outgoingoxygen, a rectification column in which air not previously liquefied insaid apparatus is liquefied and the oxygen and nitrogen are separated, aconnection with the column from which liquid oxygen may be drawn, and aliquid oxygen pump having its suction connected with said connection andits discharge leadin to said evaporator-condenser whereby liquid oxygenis supplied to the latter, the capacity of said expansion engine beingso reiated to the total compressed air supply that the mass of thecompressed air passing through said evaporator-condenser but not theexpansion engine can evaporate completely the outgoing oxygen productand be itself at least in large measure liquefied by the refrigerationproduced by vaporization of said oxygen.

26. Method of producing oxygen which includes dividing an enteringstream of air, passing one stream through an expansion engine, passinganother stream through an evaporatorcondenser in which heat exchange iseffected between but two counterfiowing streams respectively of oxygenproduct and. entering air, said second stream proportioned to supply tosaid expansion engine any unusual demand thereby for air duringoperation, liquefying in the evaporator-condenser at least a part-equalto the amount liquefiahle by the refrigeration furnished by vaporizationof oxygen product at a pressure at which its saturation temperature isclose to but below the saturation temperature of the airof the secondstream of air, liquefying any, remaining part or the second stream ofair and the first stream thereof, rectifying the liquefied air, andpumping oxygen from the rectifier, at the pressure stated, to theevaporator-condenser.

27. Method of producing oxygen at supercolumn pressure, includingconservation of refrigeration, minimization of power input, andmaintenance of stability of operation, which includes dividing anentering stream of air to be processed into two streams, passing onestream thereof through an expansion engine which is normally traversedby the major fraction of the entering air, passing another stream of theentering air, sufiicient to supply any call for air by the expansionengine under varying operating conditions, through anevaporator-condenser, rectifying both streams, and pumping the oxygenproduct, at a pressure above column pressure, through theevaporator-condenser in heat exchange relation only with the secondstream of air, the pressures of said second stream and of said oxygenbeing such that the saturation temperature of the compressed air exceedsthe saturation temperature of the oxygen by a great enough amount toeffect a sufiicient transfer of heat within the evaporator-condenser tovaporize the oxygen and liquefy an equivalent amount of the enteringair.

28. In an apparatus for the separationof gases by the rectification of amixture thereof, in combination, at least one heat exchanger, atwocourse evaporator-condenser, an expansion engine, a column having aliquid oxygen space therein, a liquid oxygen pump, means for connectingsaid at least one heat exchanger to deliver air under pressure individed streams to said evaporator-condenser and to said expansionengine, mean for delivering air exhausted from said expansion engine tosaid column, means for delivering air from said evaporatorcondenser tosaid column, means for connect ing the liquid oxygen pump with theliquid oxygen space of said column at a point to maintain the desiredliquid oxygen level therein, and means for conducting the discharge fromsaid liquidoxygen pump to said evaporator-condenser.

29. In an apparatus for the separation of gases by the rectification ofa mixture thereof, in combination, at least one heat exchanger, anevaporator-condenser having courses only for entering air and leavingoxygen product, an expansion engine, a column having a liquid oxygenspace therein, a liquid oxygen pump for raising the pressure of theoxygen product to a point at which entering air in theevaporator-condenser, by its liquefaction substantially at supplypressure, will provide the latent heat of vaporization of the liquidoxygen at the increased pressure of the latter, means for connectingsaid at least one heat exchanger to deliver air under pressure individed streams to saidevaporator-oondenser and to said expansionengine, means for delivering air exhausted from said expansion engine tosaid column, means for delivering air from said evaporator-condenser tosaid column, means for connecting the liquid oxygen pump with the liquidoxygen space of said column at a point to maintain the desired liquidoxygen level therein, and means for conducting the discharge from saidliquid oxygen pump to said evaporator-condenser.

30. In an apparatus for producing and delivering oxygen gas underpressures substantially in excess of those under which the oxygen isseparated, the combination of an expansion engine by which compressedair is cooled by expansion with the performance of work, anevaporatorcondenser having courses therein only for entering air andoutgoing oxygen and in which compressed air is liquefied by heatexchange with outgoing oxygen, a rectification column in which theoxygen and nitrogen are separated, a connection with the column fromwhich liquid oxygen may be drawn, and a liquid oxygen pump having itssuction connected with said connection and its discharge leading to saidevaporator-condenser whereby liquid oxygen is supplied to the latter,the capacity of said expansion engine being so related to the totalcompressed air supply that the mass or the compressed air passingthrough said evaporator-condenser can evaporate completely the outgoingoxygen product and be itself at least in large measure liquefied by therefrigeration produced by the evaporation of said oxygen.

31. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above atmospheric, withmaximum conservation of refrigeration, including passing the compressedair through at least one heat exchanger, dividing the air, passing aportion thereof through an expansion engine, passing another portionthereof through an evaporator-condenser, combining said portions andliquefying the same, rectifying the liquid air in a column, withdrawingliquid oxygen from the column and pumping it, at a pressure higher thanthe pressure within the rectifier, through the evaporator-condenser inheat exchange relation to the air passing through the latter andutilizing in the latter the heat of condensation of the air to vaporizein said evaporator-condenser the oxygen at its pressure substantiallyabove rectifier pressure.

32. Method of producing one of the components of a gaseous mixture as aproduct at super-column pressure, with the conservation of refrigerationand minimization of power input, which includes the rectification ofsuch component in a column, the imposition of pressure upon such productcomponent taken from the column in liquid form to bring it to a desiredsuper-column pressure, the passage of the product component so increasedin pressure through an evaporatorcondenser, and causing such portion,less than the whole, of the gaseous mixture processed to produce thedesired component to pass through such evaporator-condenser in heatexchange relation therein only with the product component, and at such apressure as to evaporate, by its own heat of condensation, such productcomponent.

33. The method of producing, by the separation of a gaseous mixture bycooling and rectification, one of the components of such mixture as aproduct at a pressure above atmospheric, with maximum conservation ofrefrigeration, including passing the gaseous mixture through at leastone heat exchanger, dividing the gaseous mixture, passing a portionthereof through an expansion engine, passing another portion thereofthrough an evaporator-condenser in heat exchange relation in the latterwith the product component only, introducing said portions into a columnand subjecting them to a rectifying process therein producing theproduct component in liquid form,

pumping said product component through the evaporator-condenser in heatexchange relation with the portion of the mixture passing through thelatter, and utilizing in said evaporator-condenser the refrigerativeefiect of evaporating product component to liquefy substantially the 28entire portion of mixture passing through said evaporator-condenser.

34. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above rectificationpressure, with maximum conservation of refrigeration, including passingthe compressed air through at least one heat exchanger, dividing theair, passing a portion thereof through an expansion engine, passinganother portion thereof through an evaporator-condenser, combining saidportions and rectifying the same in a column, withdrawing oxygen fromthe column in the liquid state and pumping it, at a pressure higher thanthe pressure within the rectifier, through the evaporator-condenser inheat exchange relation to the air passing through the latter andutilizing in the latter at least a portion of the heat of condensationof the air to vaporize the oxygen at its pressure substantially aboverectifier pressure.

35. The method of producing, by the separation of compressed air bycooling and rectification, oxygen at pressures above atmospheric, withmaximum conservation of refrigeration, including passing the compressedair through at least one heat exchanger, dividing the air, passing aportion thereof through an expansion engine, passing another portionthereof through an evaporator-condenser, combining said portions andrectifying them in a column, withdrawing oxygen from the column in theliquid state and pumping it, at a pressure higher than the pressurewithin the rectifier, through the evaporatorcondenser in heat exchangerelation to the air passing through the latter and utilizing in thelatter the heat of condensation of the air to vaporize in saidevaporator-condenser the oxygen at its pressure substantially aboverectifier pressure.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,976,388 Eichelman Oct. 9, 1934 2,408,710 Van Nuys Oct. 1,1946 2,409,458 Van Nuys Oct. 15, 1946 2,464,891 Rice Mar. 22, 19492,480,093 Anderson Aug. 23, 1949 2,480,094 Anderson Aug. 23, 19492,525,660 Fausek et al Oct. 10, 1950

